1. Field of the Invention
This application is the national phase under 35 U.S.C. §371 of PCT International Application No. PCT/EP00/01314 which has an International filing date of Feb. 18, 2000, which designated the United States of America.
The present invention relates to a bistable magnetic drive or solenoid actuator for a switch, in particular for an electric switch having an armature that works together with at least one movable switch contact and is linearly displaceable between two end positions in a space, having a shunt body formed by a magnetizable material arranged essentially on the axis of displacement of the armature and at a distance from the armature, as well as having means for generating a magnetic field which exerts a force on the armature, holding it in the end positions, in which case by combining the shunt body with the armature, the course of the flow lines of the magnetic field is altered such that the holding force acting on the armature is reduced.
2. Related Art
Magnetic drives of the respective type are usually used in the field of electric switching technology, especially in power circuit breakers which cause a rated current or an overload current to be switched on and off under specified conditions and which also isolate electric circuits from one another. Since these switches have two stable states, namely an opened state where the electric isolation of the respective circuits is maintained, and a closed state where the defined rated current flows continuously and an overload current is withstood for a certain period of time, it is necessary in particular for the drives used in the switches to also have two stable states, i.e., idle states, which necessitate holding forces.
A bistable magnetic drive for an electric switch of the type defined above is known from Unexamined German Patent No. 196 19 835, to which reference is herewith made to the full extent. This magnetic drive has an armature that is connected to at least one movable switch contact and is linearly displaceable between two end positions; the armature is held in the end positions in a stable manner under the influence of magnetically generated forces. In addition, a ferromagnetic shunt body is also provided, with the armature and shunt body being arranged in succession in a space between a first and a second stop. The stops are designed as pole faces of magnetic circuits induced by a pair of permanent magnets that hold the displaceable armature in the two stable end positions. Furthermore, there is also a pair of electromagnets whose variable magnetic fields serves to move the armature between the two stable end positions. The shunt body serves in particular to reverse the direction of the force exerted by the permanent magnet on the armature, optionally with a force exerted on the armature from the outside, by applying the shunt body to the armature, and to transfer this force to the shunt body, so that the shunt body and the armature are shifted to the second stable end position and held there.
The magnetic circuit is thus designed so that the force lines of the permanent magnets are closed outside of the armature and the shunt body, depending on whether the armature and the shunt body are arranged separately from one another or side by side, so that the force exerted by the permanent magnets is directed into one of the two directions of motion of the armature and the shunt body.
In the case of the known drive, the armature may assume two stable positions, where it is in contact with the first stop on the one end and on the other end is in contact with the shunt body, which is in turn in contact with the second stop in the second stable position of the armature. This prevents the armature which drives the movable contact from becoming “stuck” in an intermediate position between the two end positions. When the reversal of the armature positions is initiated by turning on the electromagnets or by applying the shunt body to the armature, the switching process takes place automatically and rapidly. Despite the relatively low opening energy, no stable intermediate position between the two end positions of the armature is possible, i.e., once a switching operation has been initiated, it necessarily leads to opening or closing of the switch.
It is a special requirement of the switches in question here that the fastest and most reliable shutdown, in particular in an emergency situation (“emergency cutoff”) must be guaranteed. Therefore, technically complicated additional mechanical devices (e.g., lever devices) must be provided with the known switches, so that the armature can be moved into the “OFF” position of the switch, and meanwhile the cutoff can be accomplished only at a relatively great expenditure of energy.